1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) device for use in, for example, a flat panel display, and a method of producing the device.
2. Description of the Related Art
An organic EL device being a self light-emitting device as a flat panel display has been recently attracting attention. The organic EL device is liable to cause the degradation of characteristics owing to moisture or oxygen, the organic compound layer is peeled from an electrode layer owing to a trace amount of moisture, and the peeling is responsible for the occurrence of a dark spot. In view of the foregoing, the organic EL device is covered with an etching glass cover, a sealing agent is used to bond the periphery of the resultant, and the inside of the resultant is attached with a moisture absorbent so that moisture infiltrating from a sealing surface is absorbed by the moisture absorbent. As a result, the lifetime of the organic EL device is secured.
However, the realization of a space-saving flat panel display owing to thin organic EL device requires elimination of the space for the moisture absorbent around a light-emitting area, further reduction of thickness and thus employment of a sealing method for the organic EL device without the need for a large amount of the moisture absorbent. As a result, solid sealing with a high-performance passivation layer is demanded to prevent moisture or oxygen from entering into the organic compound layer.
For solving those problems, in recent years, as a passivation layer for an organic EL device, solid sealing with an oxidized silicon nitride film using a CVD or sputtering method and a passivation layer prepared by laminating a ceramic and an organic film has been proposed.
Japanese Patent Application Laid-Open No. 2000-077183 proposes an organic EL device sealed with a passivation layer formed of a silicon nitride film by employing a plasma CVD method.
Japanese Patent Application Laid-Open No. 2002-134268 proposes a technology for a passivation layer formed of a silicon nitride film formed with a CVD method.
Further, Japanese Patent No. 3705282 proposes a technology for forming, on a device containing cesium added to an interface between an electron injection layer and an adjacent layer, a silicon nitride film or a sealing film formed of an ITO material formed by a vapor deposition method.
In general, an organic EL device is formed of an anode, an organic compound layer formed of a hole transport layer, an emission layer, an electron transport layer and an electron injection layer, a cathode, and a passivation layer for protecting these layers from moisture. In addition, the electron injection layer of the organic EL device contains an alkali metal or alkali metal compound formed by the co-vapor deposition of an organic compound material and an alkali metal compound. The electron injection layer having an alkali metal is formed as described above so that the efficiency with which an electron is injected from the layer is improved.
However, the cluster of the alkali metal compound adheres to the inside of the organic EL device upon co-vapor deposition of the alkali metal compound and the organic compound material.
The cathode of an oxide film formed of, for example, an indium tin oxide alloy (ITO), an indium zinc oxide alloy (IZO) or an indium tin zinc oxide alloy (ITZO) is formed on the electron injection layer. When the passivation layer is further formed on the cathode by using hydrogen or a material gas containing hydrogen, a void occurs on the device. The void is of a size of about several micrometers to several tens of micrometers. Further, the void may swell to burst. Such void often produces, in the passivation layer, a crack serving as a path through which moisture infiltrates, and is hence responsible for the generation of a dark spot in the organic EL device.
As described above, Japanese Patent No. 3705282 proposes a technology for forming, on an organic EL device containing cesium added to an interface between an electron injection layer and an adjacent layer, a passivation layer formed of a silicon nitride film or an ITO film with a vapor deposition method. However, foreign matter such as a cluster generated upon formation of the organic compound layer of the organic EL device by vapor deposition or the etching residue of a device isolation film adheres onto the organic EL device. The passivation layer formed of a silicon nitride film or an ITO film formed with a vapor deposition method or a sputtering method is a hard film having insufficient coverage performance, so the layer cannot completely cover the above foreign matter when the layer is formed on the foreign matter. In addition, an increase in thickness of the layer involves, for example, the following problems: a crack is generated in the layer as a sealing film, or the sealing film splinters. Accordingly, the layer does not suffice for the prevention of the infiltration of moisture or oxygen into the device.